CS 432 Object-Oriented Analysis and Design

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CS 432 Object-Oriented Analysis and Design

• Week 6
• Design Patterns
• Architecture Designs

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(No Transcript)
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Design Principles-Protection From Variations

• Parts of a system that are unlikely to change are
  segregated from those that will
• Drives the multilayer design pattern
• Stable business logic can be protected from
  variations in the user interface
• Changes in the business logic are isolated to the
  controller class

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Design Principles-Indirection

• Indirection is an implementation of the
  protection from variations principle
• Decouples classes or other system components by
  placing an intermediate classes between them
• Used in many corporate security systems between
  an internal network and the Internet
• A proxy server catches all incoming messages and
  redistributes them to the recipients

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Importance of Design Patterns

• Standard design templates can speed OO design
• Patterns can exist at different levels of
  abstraction
• At the most concrete level, a class definition
  with code
• At the most abstract level, an approach to a
  problem
• Patterns should contain five main elements
• Pattern name, problem, solution, example,
  benefits and consequences

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Pattern description for the controller pattern
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Basic Design Patterns

• The authors of Elements of Reusable
  Object-Oriented Software (referred to as the Gang
  of Four) developed a basic classification scheme
  for patterns (Figure 9-7)
• The 23 GoF patterns are some of the most
  fundamental and important patterns in use
• Scores of other patterns have been defined
• For example, both Java and .NET have sets of
  enterprise patterns

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Classification of design patterns
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Singleton Pattern

• For classes that must have only one instance, but
  need to be invoked from several classes and
  locations within the system
• The class itself controls the creation of only
  one instance
• A static variable of the class refers to the
  object that is created
• A class method instantiates the object on the
  first call, and returns a reference to the object
  on subsequent calls

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Singleton Pattern
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Singleton pattern template
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Adaptor Pattern

• Plugs an external class into a system
• Converts the method calls from within the system
  to match the method names in the external class
• A standard solution for protection from
  variations
• Insulates the system from frequently changing
  classes
• An interface is frequently used to specify and
  enforce the use of correct method names

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Adapter Pattern
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Adapter pattern template
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Design Activities in the UP Life Cycle
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Design the Support Services Architecture and
Deployment Environment

• Three organizational dispositions to new systems
• Integrate new systems into existing systems
• Install support services for the first time
• Replace existing systems
• Design issues for all organizations
• Reliability
• Security
• Throughput
• Synchronization

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Design the Software Architecture

• Software architecture refers to the big picture
  
• Two important aspects
• Division of software into classes
• Distribution of classes across processing
  locations
• Modify class diagrams into software classes
• Determine where classes and objects execute
• Determine whether they will be distributed
• Determine communication methods
• Select programming language(s) to write classes

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Design Use Case Realizations

• Use case realizations offer a lower-level view
• Two-tiered focus
• Class interactions supporting a particular use
  case
• Interactions among software, users, and external
  systems
• Design typically spread over many iterations
• UML design class diagrams and interaction
  diagrams document design

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Design the Database

• Designing database as a key design activity
• Physical model of database based on class diagram
• Physical model describes relational or OO
  database
• Some technical issues
• Performance, such as response time
• Integration with existing databases
• Legacy databases

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Design the System and User Interfaces

• System interface issues
• Different types of systems will interface
• Systems interact with internal and external users
  
• User interface issues
• User capabilities and needs differ widely
• User interacts with the system in different ways
• Approaches to interface vary by system
• Has nature of interface emerged from earlier
  models?

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Design the System Security and Controls

• User-interface controls limit access to
  authorized users
• System interface controls protect system from
  other systems
• Application controls record transactions and
  validate work
• Database controls ensure data protected from
  unauthorized access and accidental loss
• Network controls protect network communication

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Design Activities and the UP

• Focus in early iterations of elaboration phase
• System architecture and databases
• Evenly distributed throughout project
• Detailed design activities
• Criteria analyst uses to schedule design
  activities
• Experience
• Forecasting capabilities
• Every design impacts other parts of system

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Single-Computer and Multitier Architecture

• Single-computer architecture
• Single system attached to peripheral devices
• PC and mainframe applications qualify
• Advantages easy to design, build, operate,
  maintain
• Disadvantages capacity limits

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Single-computer, Clustered, and
Multicomputer Architectures
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Single-Computer and Multitier Architecture
(continued)

• Multitier architecture (multiple computer
  systems)
• Clustered architecture
• Group of computers logically operate as one
• Nodes from same manufacturer and model family
• Multicomputer architecture
• Cluster whose nodes are optimized or specialized
• Hardware and operating systems may be dissimilar

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Centralized and Distributed Architecture

• Centralized architecture
• Deploys computer systems in single location
• Used for large-scale processing applications
• Constraint geography
• Implements subsystems in larger information
  system
• Distributed architecture
• Software/data spread across systems and locations
• Relies on communication networks to interconnect

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Client/Server Architecture

• Client/server architecture tiers
• Client requests resources or services from a
  server
• Server manages information system resources
• Architectural issues for client/server software
• Decomposing software into client and server
  programs (objects)
• Determining where clients and servers will
  execute
• Describing interconnection protocols and networks
  

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Client/Server Architecture with a Shared
Database
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Client/Server Architecture(continued)

• Client and server communicate via well-defined
  protocols over a physical network
• Client/server architecture advantages
• Location flexibility, scalability,
  maintainability
• Client/server architecture disadvantages
• Additional complexity, potential poor
  performance, security issues, and reliability 

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Interaction Among Multiple Clients and a
Single Server
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Three-Layer Client/Server Architecture

• Variant of client/server architecture
• Divides application software into independent
  processes
• Three-layers
• The data layer
• The business logic layer
• The view (presentation) layer
• Three-tier architecture advantages
• Additional flexibility and reliability

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Three-Tier Logical Layers
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Three-Tier Architecture
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Four-Tier Architecture
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Model-View-Controller (MVC)Design Pattern or
Framework
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Middleware

• Middleware
• Connects parts of an application
• Enables requests and data to pass among them
• Common types of middleware
• Teleprocessing monitors
• Transaction processing monitors
• Object request brokers (ORBs)
• Each type of middleware has its own set of
  protocols

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Differences between client/server and
Internet systems
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Web Client/Server Architecture
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Internet and Web-Based Software Architecture

• Web is complex example of client/server
  architecture
• Web resources are managed by server processes
• Clients are programs that send requests to
  servers
• Web protocols define valid resource formats and
  communication standards
• Web-like capabilities embedded in ordinary
  applications
• Web-oriented client/server architecture
  service-oriented architecture (SOA)  

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Internet and Web-Based Software Architecture
(continued)

• Flexibility is the key to the Internet
  alternative
• Accessibility, low cost communication, widely
  used standards
• Disadvantages of Web technologies
• Security, reliability, throughput, and volatile
  standards
• The key architectural design issues
• Defining client and server processes or objects
• Distributing processes across hardware platforms
• Connecting processes

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Simple Internet Architecture

• Used for viewing static information
• The browser component executes on the client
  computer
• The Internet server component executes on the
  server computer
• Pages reside on the server and are sent to the
  browser for display
• Program logic is inserted through scripting
  languages (JavaScript, VBScript), applets, or
  other controls

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Simple Internet architecture
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Two-layer Architecture

• Primarily captures information from the user and
  updates the database
• The domain layer and data access layer are
  usually combined
• Input data is sent to a CGI or an application
  server
• The user-interface classes often contain the
  business logic and data access
• Processing takes place with servlets (Java) or
  code behind classes (.NET)

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Two-layer Internet architecture
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Three-layer Architecture

• Separates domain layer and data access layers
• Necessary for systems with complex business logic
  or multiple user interfaces
• Using CGI
• Provide a use case controller for each form that
  distributes messages to the individual objects of
  the system.
• Using an application server
• Java tools Java Server Pages and servlets
• .NET tools Common Runtime Language and code
  behind classes

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Three-layer Internet architecture
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Invoking a Web service
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Designing Enterprise-level Systems

• Enterprise-level systems share components among
  multiple people or groups in an organization
• Enterprise-level systems almost always use
  multiple tiers of computers
• Can be client/server network-based or Internet
  based
• Designed with deployment diagrams
• A type of implementation diagram that shows
  physical components across different locations